This invention relates to a building construction system, and more particularly to a so-called curtain wall and window construction system for a steel or concrete frame office or other commercial buildings.
Oftentimes, commercial buildings, such as office buildings, high rise apartment buildings, hotels, and the like, utilize a skeletal framework of steel or concrete beams. Framing studs are secured to the framework of the building along the exterior portions thereof and so-called curtain walls are secured to this framework so as to constitute the exterior walls and windows of the building. Typically, these curtain walls comprise exterior wall panels having an outer metal sheet which has been treated to give a desired surface finish, an inner metal sheet, and a thermal insulative core between the inner and outer sheets. The exterior wall panels are typically so arranged on the exterior wall of the building as to form window openings therein for receiving glass panels which are oftentimes sealed in place relative to the exterior wall panels. Reference may be made to such as U.S. Pat. Nos. 2,885,040, 3,715,848, 3,319,388, 3,316,681 which show various typical prior art curtain wall constructions.
In recent years, it has become particularly desirable, so as to create a desired aesthetic effect for a building, to have substantially continuous expanses of the exterior walls of large commercial buildings with as little break as possible between the adjacent wall panels or between the adjacent window panes. In particular, it has been desirable on the part of many architects to omit both vertical and horizontal exterior framing, furring members, mullions, or stanchions which were heretofore utilized along the horizontal and vertical joints of adjacent wall panels or window panes so as to aid in the securement of the exterior wall panels and the window panes to the frame of the building. A typical prior curtain wall construction which utilized exterior supports at the intersections of all of the exterior wall panels and window panes is illustrated in the above-mentioned prior U.S. Pat. No. 2,885,040.
However, since the exterior mullions, stanchions, or other framing members are desirably omitted on many modern building designs, there has been a problem in how to economically form the panels and the windows for the exterior walls of the building, to eliminate the stanchions or mullions, and yet to securely fasten the exterior wall panels and window panes to the frame of the building.
Still further, in many modern buildings which have a large glass window area, condensation and other moisture often builds up on the interior surfaces of the windows and collects at the bottoms thereof. As shown in U.S. Pat. No. 1,320,084, it was known to utilize a drain tube at the base of a large plate glass window in a store front so that condensation accumulating at the bottom, inner face of the window may be drained to the outside of the building below the windowsill. However, such a weep duct which exited directly to the outside face of the window immediately below the sill would break up the uniform appearance of the exterior panels of the building.
Additionally, since it is quite conventional in buildings of curtain wall construction to construct the exterior wall panels of metal sheeting with an insulative core therebetween, these metal panels will tend to expand and contract to a substantial degree relative to the building framework and relative to the glass windowpane when the exterior walls are subjected to varying temperature extremes, such as during extremely cold winter days or such as when exposed to direct sunlight. Also, in order to achieve an advantageous thermal efficiency for the walls of the building, it is important that the exterior walls of the building be effectively sealed against both water vapor and air exchange with the outside air.